skygazer’s almanac for latitudes near 40° nort 2012h sga ...€¦ · mar 26 venus reaches...

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SGA 2012 (North America)S

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Jan 5

Jan 8

Mar 20

Apr 18

Jun 4

Jun 13Jun 17

Jul 9

Aug 15

Aug 16

Sep 22

Oct 3

Nov 14 Nov 27 Dec 4

Dec 21

MORNING SKY

MORNINGeveNING A supplement to Sky & teleScope

Jan 4 Earth is 91,401,967 miles from the Sun (perihelion) at 7 p.m. EST

Feb 9 Uranus lies just 0.3° below Venus

Mar 3 Mars is at opposition tonight

Mar 4 Mercury attains greatest elongation, 18° east of the Sun

Mar 26 Venus reaches greatest elongation, 46° east

Apr 14 Saturn is at oppositionMay 20 An annular eclipse of the

Sun occurs in a path from California to Texas, after beginning (on the 21st locally) in eastern China, Japan, and the north Pacific

Jun 5 A rare transit of Venus over the Sun is widely visible, especially from North America, the Pacific Ocean, and (on the 6th) Asia and Australia

Jun 20 Longest day, 15h 01m at latitude 40° north; summer begins at the solstice, 7:09 p.m. EDT

Jun 24 Latest twilightJun 27 Latest sunsetJun 30 Mercury attains greatest

elongation, 26° eastJul 4 Earth is 94,505,851 miles from

the Sun (aphelion) at 11 p.m. EDT

Aug 23 Neptune’s oppositionSep 28 Uranus’s oppositionOct 26 Mercury 24° east of SunNov 28 A penumbral lunar

eclipse, with most shading at 14:33 UT, for the Far East and Australia

Dec 2 Jupiter’s opp.Dec 4 Earliest end of

twilightDec 7 Earliest

sunsetDec 21 Shortest

day of year, 9h 20m

eveNING SKYLatest

sunrise of the year at latitude

40° northLatest onset of

morning twilight Spring begins

at the equinox, 1:14 a.m. EDT

Mercury is at greatest elongation, 27° west of

the SunThe Moon is partially

eclipsed in the Americas from 2:59 to 5:07 a.m. PDT,

and on the evening of the 4th in Australia and the Far East

Earliest sunriseEarliest morning twilight

Aldebaran is 0.9° to the lower right of Venus Venus attains greatest elongation, 46° west of the SunMercury is at greatest elongation, 19° west of the SunFall begins at the equinox, 10:49 a.m. EDTRegulus is just 0.2° above Venus!A total eclipse of the Sun occurs in a path across northernmost Australia and into the South Pacific Ocean (where it becomes the afternoon of the 13th)Saturn is 0.8° above Venus Mercury is at greatest elongation, 21° west of the SunWinter begins at the solstice, 6:12 a.m. EST

Computed by Roger W. Sinnott. © 2012 Sky & Telescope Media, LLC. Printed in USA.

Sky & Telescope 90 Sherman St. Cambridge, MA 02140 USA

®

Sk yandTe lescope .com

Skygazer’sAlmanac 2012FOR LATiTUDES NEAR 40° NORTh

SGA12R

When does the Sun set, and when does twilight end? Which planets are visible? What time does the Moon rise?

Welcome to the Skygazer’s Almanac 2012 — a handy chart that answers these and many other questions for every night of the year. It is plotted for skywatchers near latitude 40° north — in the United States, Mediterranean coun-tries, Japan, and China.

For any date, the chart tells the times when astronomical events occur during the night. Dates on the chart run verti-cally from top to bottom. Time of night runs horizontally, from sunset at left to sunrise at right. Find the date you want on the left side of the chart, and read across toward the right to find the times of events. Times are labeled along the chart’s top and bottom.

In exploring the chart you’ll find that its night-to-night patterns offer many insights into the rhythms of the heavens.

The Events of a Single NightTo learn how to use the chart, consider some of the events of one night. We’ll pick January 15, 2012.

First find “January” and “15” at the left edge. This is one of the dates for which a string of fine dots crosses the chart horizontally. Each horizontal dot-ted line represents the night from a Sun-day evening to Monday morning. The individual dots are five minutes apart.

Every half hour (six dots), there is a vertical dotted line to aid in reading the hours of night at the chart’s top or bottom. On the vertical lines, one dot is equal to one day.

A sweep of the eye shows that the line for the night of January 15–16 crosses

many slanting event lines. Each event line tells when something happens.

The dotted line for January 15–16 begins at the heavy black curve at left, which represents the time of sunset. Reading up to the top of the chart, we find that sunset on January 15th occurs at 4:59 p.m. Local Mean Time. (All times on the chart are Local Mean Time, which can differ from your standard clock time. More on this later.)

Moving to the right, we see that the bright star Sirius rises at 6:02 p.m. At 6:18 Jupiter transits the meridian, mean-ing the giant planet is then due south and highest in the sky. Evening twilight ends at 6:34, marking the time when the Sun is 18° below the horizon.

At about 7:08 p.m. Polaris, the North Star, is at upper culmination. This is when Polaris stands directly above the north celestial pole (by 41′ this year), a good time to check the alignment of an equatorial telescope. The dim planet Neptune sets at 7:48, so we can cross it off the observing list tonight.

Brilliant Venus, after being promi-nent in the western sky, sets at 8:01. But the red planet Mars rises at 9:35. Then the Great Orion Nebula, M42, transits at 9:56, as does Sirius at 11:05. Transits of celestial landmarks help indicate where the constellations are during the night.

Running vertically down the mid-night line is a scale of hours. This shows the sidereal time (the right ascension of objects on the meridian) at midnight. On January 15–16 this is 7h 40m. To find the sidereal time at any other time and date on the chart, locate that point and draw a line through it parallel to the white event lines of stars. See where your line inter-sects the sidereal-time scale at midnight. (A star’s event line enters the top of the chart at the same time of night it leaves

the bottom. Sometimes one of these seg-ments is left out to avoid crowding.)

Near the midnight line is a white curve labeled Equation of time weaving narrowly down the chart. If you regard the midnight line as noon for a moment, this curve shows when the Sun crosses the meridian and is due south. On Janu-ary 15th the Sun runs slow, transiting at 12:09 p.m. This variation is caused mainly by the tilt of Earth’s axis.

At 12:28 a.m. the Moon rises, and we can tell by its large symbol that it is at Last Quarter. Saturn rises just 10 min-utes later — a good clue that it and the Moon are fairly close in the sky.

Jupiter finally leaves the sky at 12:57 a.m. But Mars transits at 3:58, so we know this planet is best placed for tele-scopic viewing toward dawn. Then a star we usually associate with a much later season, Antares, rises at 4:24.

The first hint of dawn — the start of morning twilight — comes at 5:44 a.m. Saturn transits at 6:10, and elusive Mer-cury rises in the east at 6:36. The Sun finally peeks above the horizon at 7:20 a.m. on the morning of January 16th.

Other Charted InformationMany of the year’s chief astronomical events are listed in the chart’s evening and morning margins. Some are marked on the chart itself.

Conjunctions (close pairings) of two planets are indicated on the chart by a symbol on the planets’ event lines. Here, conjunctions are considered to occur when the planets actually appear closest together in the sky (at appulse), not merely when they share the same ecliptic longitude or right ascension.

Opposition of a planet, the date when it is opposite the Sun in the sky and thus visible all night, occurs when its transit

What’s in the sky tonight?

Skygazer’sAlmanac 2012for latitudes near 40° north

Skygazer’s Almanac 2012 is a supplement to

Sky & Telescope. © 2012 Sky & Telescope Media, LLC.

All rights reserved.

For reprints (item SGA12R, $4.95 each postpaid) or

to order a similar chart for latitude 50° north or 30°

south, contact Sky & Telescope, 90 Sherman St.,

Cambridge, MA 02140, USA; phone 800-253-0245,

fax 617-864-6117. You can

send e-mail to custserv@

SkyandTelescope.com, or

visit our online store at

SkyandTelescope.com.

®

Rising or Setting Corrections

Declination (North or South)

0° 5° 10° 15° 20° 25°

50° 0 7 14 23 32 43

45° 0 3 7 10 14 19

40° 0 0 0 0 0 0

35° 0 3 6 9 12 16

30° 0 5 11 16 23 30

25° 0 8 16 24 32 42

Atlanta +38 Boise +45 Boston –16 Buffalo +15 Chicago –10 Cleveland +27 Dallas +27 Denver 0Detroit +32El Paso +6Helena +28Honolulu +31Houston +21Indianapolis +44Jacksonville +27Kansas City +18

Los Angeles –7Memphis 0Miami +21Minneapolis +13New Orleans 0New York –4Philadelphia +1 Phoenix +28Pittsburgh +20St. Louis +1Salt Lake City +28San Francisco +10Santa Fe +4Seattle +10 Tulsa +24Washington +8

Local Mean Time Corrections

Athens +25Baghdad +3Beijing +14Belgrade –22Cairo –8Istanbul +4Jerusalem –21

Lisbon +36Madrid +75New Delhi +21Rome +10Seoul +32Tehran +4Tokyo –19

line crosses the Equation-of-time line (not the line for midnight). Opposition is marked there by a symbol, as for Mars on the night of March 3–4.

Moonrise and moonset can be told apart by whether the round limb — the outside edge — of the Moon symbol faces right (waxing Moon sets) or left (waning Moon rises). Or follow the nearly horizontal row of daily Moon symbols across the chart to find the word Rise or Set. Quarter Moons are indicated by a larger symbol. Full Moon is always a large bright disk whether rising or setting; the circle for new Moon is open. P and A mark dates when the Moon is at perigee and apogee (nearest and farthest from Earth, respectively).

Mercury and Venus never stray far from the twilight bands. Their dates of greatest elongation from the Sun are shown by ◗ symbols on their rising or setting curves. Asterisks mark the dates when Mercury and Venus show their greatest illuminated extent in square arcseconds. For Venus, but not Mercury, it is also the date of greatest brilliancy.

Meteor showers are marked by a star-burst symbol at the date of peak activity and at the time when the shower’s radi-ant is highest in the night sky. This is often just as morning twilight begins.

Julian dates can be found from the numbers just after the month names on the chart’s left. The Julian day, a seven-digit number, is a running count of days beginning with January 1, 4713 BC. Its first four digits early this year are 2455, as indicated just off the chart’s upper-left margin. To find the last three digits for evenings in January, add 927 to the date. For instance, on the evening of January 15th we have 927 + 15 = 942, so the Julian day is 2,455,942. For North American observers this number applies all night, because the next Julian day always begins at 12:00 Universal Time (6:00 a.m. Central Standard Time).

Time CorrectionsAll events on this Skygazer’s Almanac are plotted for an observer at 90° west longitude and 40° north latitude, near the population center of North America. However, you need not live near Peoria, Illinois, to use the chart. Simple correc-tions will allow you to get times accu-

rate to a couple of minutes anywhere in the world’s north temperate latitudes.

To convert the charted time of an event into your civil (clock) time, the following corrections must be made. They are given in decreasing order of importance:

• daylight-saving time. When this is in effect, add one hour to any time obtained from the chart.

• your longitude. The chart gives the Local Mean Time (LMT) of events, which differs from ordinary clock time by a number of minutes at most loca-tions. Our civil time zones are standard-ized on particular longitudes. Examples in North America are Eastern Time, 75° W; Central, 90°; Mountain, 105°; and Pacific, 120°. If your longitude is very close to one of these (as is true for New Orleans and Denver), luck is with you

and this correction is zero. Otherwise, to get standard time add 4 minutes to times obtained from the chart for each degree of longitude that you are west of your time-zone meridian. Or subtract 4 minutes for each degree you are east of it.

For instance, Washington, DC (longi-tude 77°), is 2° west of the Eastern Time meridian. So at Washington, add 8 min-utes to any time obtained from the chart. The result is Eastern Standard Time.

Find your time adjustment and memorize it; you will use it always. The table below shows the corrections from local to standard time, in minutes, for some major cities.

• rising and setting. Times of rising and setting need correction if your lati-tude differs from 40° north. This effect depends strongly on a star or planet’s declination. (The declinations of the Sun and planets are given in Sky & Telescope.)

If your site is north of latitude 40°, then an object with a north declination stays above the horizon longer than the chart shows (it rises earlier and sets later), while one with a south declination spends less time above the horizon. At a site south of 40°, the effect is just the reverse. Keeping these rules in mind, you can gauge the approximate number of minutes by which to correct a rising or setting time from the table above.

Finally, the Moon’s rapid orbital motion alters lunar rising and setting times slightly if your longitude differs from 90° west. The Moon rises and sets about two minutes earlier than the chart shows for each time zone east of Central Time, and two minutes later for each time zone west of Central Time. Euro-pean observers can simply shift each rising or setting Moon symbol leftward a quarter of the way toward the one for the previous night.

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A supplement to Sky & teleScope

MORNING SKYEVENING SKYFeb 9 Uranus lies

0.6° to the upper left of Venus

Mar 3 Mars is at opposition tonight

Mar 5 Mercury attains greatest elongation, 18° east of the Sun

Mar 26 Venus reaches greatest elongation, 46° east of the Sun

Apr 15 Saturn is at opposition tonight

May 20 An annular eclipse of the Sun occurs in a path that crosses the western United States, after beginning (on the morning of the 21st locally) in easternmost China, Japan, and the northern Pacific Ocean

Jun 5 A rare transit of Venus over the Sun is widely visible, especially from North America, the Pacific Ocean, and (on the 6th) Asia and Australia

Jun 20 Longest day, 16h 22m at latitude 50° north; summer begins at the solstice, 23:09 UT

Jun 25 Latest sunsetJun 30 Mercury attains greatest elongation, 26°

east of the SunAug 13 Spica shines 1.8° below Mars Aug 24 Neptune is at opposition tonightSep 22 Fall begins at the equinox, 14:49 UTSep 28 Uranus is at opposition tonightOct 26 Mercury attains greatest elongation,

24° east of the SunNov 28 A penumbral eclipse of the Moon,

with the northern limb most shaded at 14:33 UT, is best seen from the Far East and Australia

Dec 2 Jupiter is at opposition tonight

Dec 8 Earliest end of evening twilight

Dec 11 Earliest sunsetDec 21 Shortest day, 8h 04m

at latitude 50° north

Jan 1

Jan 3

Jan 5

Mar 20

Apr 19

Jun 4

Jun 16Jul 5

Jul 9

Aug 15 Aug 16 Oct 3 Nov 14 Nov 27Dec 5

Dec 21

Computed by Roger W. Sinnott. © 2012 Sky & Telescope Media, LLC. Printed in USA.

Sky & Telescope 90 Sherman St. Cambridge, MA 02140

USA

MORNINGEVENING

Latest sunrise of

the yearLatest onset of

morning twilightEarth is 147,097,207

km from the Sun (perihelion) at 0h UT

Spring begins at the equinox, 5:14 UT

Mercury is at greatest elongation, 27° west of

the SunThe Moon is partially eclipsed

from 9:59 to 12:07 UT, which is before dawn in the Americas

and on the evening of the 4th in Australia and the Far East

Earliest sunrise at latitude 50° northEarth is 152,092,424 km from the Sun

(aphelion) at 3h UTAldebaran is 0.9° to the lower right of Venus Venus attains greatest elongation, 46° west of the SunMercury is at greatest elongation, 19° west of the SunRegulus is just 0.1° to the left of Venus! A total eclipse of the Sun occurs in a path across northernmost Australia and into the South Pacific Ocean (where it becomes the afternoon of the 13th)

Saturn is 0.6° above Venus Mercury is at greatest elongation,

21° west of the SunWinter begins at the solstice,

11:12 UT

®


Skygazer’sAlmanac 2012FOR LATiTUDES NEAR 50° NORTh


SGA12E


When does the Sun set, and when does twilight end? Which planets are visible? What time does the Moon rise?

Welcome to the Skygazer’s Almanac 2012 — a handy chart that answers these and many other questions for every night of the year. This version is plotted for skywatchers near latitude 50° north — in the United Kingdom, northern Europe, Canada, and Russia.


In exploring the chart you’ll find that its night-to-night patterns offer many insights into the rhythms of the heavens.

The Events of a Single NightTo learn how to use the chart, consider the events of one night. We’ll pick Janu-ary 15, 2012.





The dotted line for January 15–16 begins at the heavy black curve at left, which represents the time of sunset. Reading up to the top of the chart, we find that sunset on January 15th occurs at 4:26 p.m. Local Mean Time. (All times on the chart are Local Mean Time, which can differ from your standard clock time by many minutes. More on this later.)

Moving to the right, we see that Jupiter transits at 6:19 p.m., meaning it is then due south and highest in the sky. Evening twilight ends at 6:22, marking the time when the Sun is 18° below the horizon. Then at 6:27 the brilliant star Sirius rises.

At about 7:09 Polaris, the North Star, reaches upper culmination. This is when Polaris stands directly above the north celestial pole (by 41′ this year), a good opportunity to check the alignment of an equatorial telescope.

The faint telescopic planet Neptune sets at 7:32, so we can cross it off the observing list. Venus follows it down at 7:43. But the Pleiades transit the merid-ian at 8:09. At 9:27 the red planet Mars rises, and then the famous Orion Nebula transits at 9:57, as does Sirius at 11:06. Transits of celestial landmarks help indicate where the constellations are throughout the night.

Running vertically down the mid-night line is a scale of hours. This shows the sidereal time (the right ascension of objects on the meridian) at midnight. On January 15–16 this is 7h 39m. To find the sidereal time at any other time and date on the chart, locate the point for the time and date you want, then draw a line through it parallel to the white event lines of stars. See where your line inter-sects the sidereal-time scale at midnight. (A star’s event line enters the top of the

chart at the same time of night it leaves the bottom. Sometimes one of these seg-ments is left out to avoid crowding.)

Near the midnight line is a white curve labeled Equation of time weaving narrowly right and left down the chart. If you regard the midnight line as the previous noon for a moment, this curve shows when the Sun crosses the merid-ian and is due south. On January 15th the Sun runs slow, transiting at 12:09 p.m. This variation is caused mainly by the tilt of Earth’s axis.

At 12:29 a.m. the Moon rises, and we can tell from the large symbol it is at Last Quarter. Saturn rises at 12:52, and Jupiter finally sets at 1:14. Mars transits at 3:59, so we know it is then best placed for telescopic viewing. (It will be brighter and closer to Earth in two months, when it transits near midnight.) Then a star that we usually associate with later sea-sons, Antares, rises at 5:11.

The first hint of dawn — the start of morning twilight — comes at 5:57 a.m. We might even glimpse elusive Mercury

Amsterdam +40 Belfast +24 Berlin +6Bordeaux +62 Bremen +24 Brussels +44 Bucharest +16 Budapest –16Calgary +36 Copenhagen +10 Dublin +25 Geneva +35 Glasgow +16Halifax +14 Hamburg +20 Helsinki +20 Kiev –2 London 0 Lyons +41

Manchester +8Montreal –6Moscow +26Munich +14Oslo +17Ottawa +3Paris +51Prague +2Quebec –15Regina +58Reykjavik +88St. John’s +1Stockholm –12Toronto +18Vancouver +12Vienna –5Warsaw –24Winnipeg +29Zurich +24

Skygazer’sAlmanac 2012for latitudes near 50° north


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after it rises at 7:14. The Sun finally peeks above the horizon at 7:52 a.m. on the morning of January 16th.

Other Charted InformationMany of the year’s chief astronomical events are listed in the chart’s evening and morning margins. Some are marked on the chart itself.


Opposition of a planet, the date when it is opposite the Sun in the sky and thus visible all night, occurs when its transit line crosses the Equation-of-time line (not the line for midnight). Opposition is marked there by a symbol. For instance, Mars reaches opposition on the night of March 3–4.

Moonrise and moonset can be told apart by whether the round limb — the outside edge — of the Moon symbol faces right (waxing Moon sets) or left (waning Moon rises). Or follow the nearly horizontal row of daily Moon symbols across the chart to find the word Rise or Set. Quarter Moons are indicated by a larger symbol. Full Moon is always a large bright disk whether rising or setting; the circle for new Moon is open. P and A mark dates when the Moon is at perigee and apogee (nearest and farthest from Earth, respectively).

Mercury and Venus never stray far from the twilight bands. Their dates of greatest elongation from the Sun are shown by ◗ symbols on their rising or setting curves. Asterisks mark the dates when Mercury and Venus show their greatest illuminated extent in square arcseconds. This is also when Venus, but not Mercury, is at greatest brilliancy.

Meteor showers are marked by a star-burst symbol at the date of peak activity and the time when the shower’s radiant is highest in the night sky. This is often just as twilight begins before dawn.

Julian dates can be found from the numbers just after the month names on the chart’s left. The Julian day, a seven-digit number, is a running count

of days beginning with January 1, 4713 BC. Its first four digits early this year are 2455, as indicated just off the chart’s upper-left margin. To find the last three digits for evenings in January, add 927 to the date. For instance, on the evening of January 15th we have 927 + 15 = 942, so the Julian day is 2,455,942. For European observers this number applies all night, because the next Julian day always begins at 12:00 Universal Time (noon Greenwich Mean Time).

Time CorrectionsAll events on this Skygazer’s Almanac are plotted for an observer at 0° longi-tude and 50° north latitude, a reason-able compromise for the countries of northern and central Europe. However, you need not be on a boat in the English Channel to use the chart. Simple correc-tions will allow you to get times accurate to a couple of minutes anywhere in the world’s north temperate latitudes.

To convert the charted time of an event into your civil (clock) time, the following corrections must be made. They are given in decreasing order of importance:

• daylight-saving time (or “summer time”). When this is in effect, add one hour to any time that you obtain from the chart.

• your longitude. The chart gives the Local Mean Time (LMT) of events, which differs from ordinary clock time by a number of minutes at most locations. Our civil time zones are standardized on particular longitudes. Examples in Europe are Greenwich Mean Time (or Universal Time), 0°; Central European Time, 15° E; and East European Time, 30°. If your longitude is very close to one of these (as is true for London), luck is with you

and this correction is zero. Otherwise, to get standard time add 4 minutes to times obtained from the chart for each degree of longitude that you are west of your time-zone meridian. Or subtract 4 minutes for each degree you are east of it. You can look up your longitude on a map.

For instance, Copenhagen (longitude 12.5° east) is 2.5° west of the Central European Time meridian. So at Copen-hagen, add 10 minutes to any time obtained from the chart. The result is Central European Standard Time.

Find your local-time correction and memorize it; you will use it always. In the table below at left are the corrections from local to standard time, in minutes, for some major cities.

• rising and setting. Times of rising and setting need correction if your lati-tude differs from 50° north. This effect depends strongly on a star or planet’s declination. (The changing declinations of the Sun and planets can be found in each issue of Sky & Telescope.)

If your site is north of latitude 50°, then an object with a north declination stays above the horizon longer than the chart shows (it rises earlier and sets later), while one with a south declination spends less time above the horizon. At a site south of 50°, the effect is just the reverse. Keeping these rules in mind, you can gauge the approximate number of minutes by which to correct a rising or setting time from the table at upper left.

Finally, the Moon’s rapid orbital motion alters lunar rising and setting times slightly if your longitude differs from 0°. The Moon rises and sets about two minutes earlier than the chart shows for each time zone east of Green-wich Mean Time, and two minutes later for each time zone west of Greenwich Mean Time.


0° 5° 10° 15° 20° 25°

60° 1 11 23 36 53 80

55° 0 5 10 16 23 32

50° 0 0 0 0 0 0

45° 0 4 8 13 18 24

40° 1 8 15 23 32 43

35° 1 10 20 31 44 68

30° 1 12 25 39 54 72

25° 1 15 30 46 64 84




For reprints (item SGA12E, $5.95 each postpaid) or

to order a similar chart for latitude 40° north or 30°

south, contact Sky & Telescope, 90 Sherman St.,

Cambridge, MA 02140, USA; phone +1 617-864-

7360, fax +1 617-864-6117.

Send e-mail to custserv@

SkyandTelescope.com, or



®

SkyandTelescope.com

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Jan 4 Latest twilight of the year (lat. 30° south)Jan 10 Latest sunsetFeb 10 Uranus lies 0.4° to the upper left of VenusMar 3 Mars is at opposition tonightMar 5 Mercury attains greatest elongation, 18°

east of the SunMar 20 Fall begins at the equinox, 3:14 p.m. ESTMar 27 Venus attains greatest elongation, 46°

east of the SunApr 15 Saturn comes to opposition tonightJun 4 The Moon is partially eclipsed for

Australia from 7:59 to 10:07 p.m. EST, and before dawn on the 4th in the Americas

Jun 7 Earliest end of evening twilightJun 10 Earliest sunsetJun 21 Shortest day, 10h 13m at latitude 30°

southJul 1 Mercury attains greatest

elongation, 26° east of the SunJul 5 Earth is 152,092,424 km from

Sun (aphelion) at 1 p.m. ESTAug 14 Spica is 1.8° left of Mars Aug 24 Neptune is at oppositionSep 29 Uranus is at oppositionOct 26 Mercury attains greatest

elongation, 24° east of the Sun

Nov 28 A penumbral eclipse of the Moon, with the northern limb most shaded at 14:33 UT, is best seen from the Far East and Australia around local midnight

Dec 2 Jupiter is at opposition

Dec 21 Longest day, 14h 05m at latitude 30° south; summer begins at the solstice, 9:12 p.m. EST

morning SKY

Jan 5 Earth is 147,097,207 km from the Sun (perihelion) at 10 a.m. EST

Apr 19 Mercury is at greatest elongation, 27° west of the Sun

May 21 An annular eclipse of the Sun occurs in a path from easternmost China across Japan, the northern Pacific Ocean, and the western United States (on the afternoon of the 20th there)

Jun 6 A rare transit of Venus over the Sun is widely visible in Asia and Australia, and also (on the 5th local time) in Hawaii and North America

Jun 21 Winter begins at the solstice, 9:09 a.m. EST

Jul 1 Latest sunriseJul 4 Latest onset of morning

twilightJul 10 Aldebaran is 0.9° to the

upper right of Venus Aug 16 Venus attains greatest

elongation, 46° west of the Sun

Aug 17 Mercury is at greatest elongation, 19° west of the Sun

Sep 23 Spring begins at the equinox, 12:49 a.m. EST

Oct 4 Regulus is 0.6° to the upper left of Venus

Nov 14 A total eclipse of the Sun occurs in a path across northernmost Australia and into the South Pacific Ocean (where it becomes afternoon on the 13th)

Nov 27 Saturn is 0.6° below Venus Dec 3 Earliest sunriseDec 5 Mercury stands at greatest elongation,

21° west of the SunDec 8 Earliest morning twilight

Computed by Roger W. Sinnott. © 2012 Sky &

Telescope Media, LLC. Printed in USA.

Sky & Telescope 90 Sherman St. Cambridge, MA 02140 USA

A supplement to Sky & teleScope

®


Skygazer’sAlmanac 2012FOR LATiTUDES NEAR 30° SOUTH

SGA12S


When does the Sun set, and when does twilight end? Which planets are visible? What time is moonrise?

Welcome to the Skygazer’s Almanac 2012 — a handy chart that answers these and many other questions for every night of the year. This version is plotted for skywatchers near latitude 30° south — in Australia, southern Africa, and the southern cone of South America.


In exploring the chart, you’ll find that its night-to-night patterns offer many insights into the rhythms of the heavens.

The Events of a Single NightTo learn how to use the chart, consider the events of one night. We’ll pick Janu-ary 15, 2012.





The dotted line for January 15–16 begins at the heavy black curve at left, which represents the time of sunset. Reading up to the top of the chart, we find that sunset on January 15th occurs at 7:05 p.m. Local Mean Time. (All times read from the chart are Local Mean Time, which can differ from your standard clock time by many minutes. More on this later.)

Moving to the right, we see that at 8:11 p.m. the Pleiades transit the merid-ian, meaning the famous star cluster is then highest in the sky. Evening twilight ends at 8:39, marking the time when the Sun is 18° below the horizon.

Dim Neptune sets at 9:01 p.m., so we can cross it off the observing list. Venus follows it down 10 minutes later.

The Large Magellanic Cloud culmi-nates (another way of saying it transits) at 9:46. Then the Great Orion Nebula transits at 9:58. Transit times of celestial landmarks keep us aware of the march of constellations through the night sky.

The red planet Mars rises at 10:12, so we know it will be well placed for tele-scopic views in the predawn hours. The Moon rises at 10:46, and we can see from its symbol that it is at waning gibbous phase. The two brightest nighttime stars, Canopus and Sirius, transit at 10:47 and 11:08, respectively. Then Saturn rises in the east at 11:50, just before Jupiter sets.

Running vertically down the mid-night line is a scale of hours. This shows the sidereal time (the right ascension of objects on the meridian) at midnight. On January 15–16 this is 7h 38m. To find the sidereal time at any other time and date on the chart, locate the point for the time and date you want, then draw a line through it parallel to the white event

lines of stars. See where your line inter-sects the sidereal-time scale at midnight. (A star’s event line enters the top of the chart at the same time of night it leaves the bottom. Sometimes one of these seg-ments is left out to avoid crowding, but it can be drawn in.)

Near the midnight line is a white curve labeled Equation of time weaving narrowly right and left down the chart. If you regard the midnight line as the previous noon for a moment, this curve shows when the Sun crosses the merid-ian and is due north. On January 15th the Sun runs slow, transiting at 12:09 p.m. This variation is caused mainly by the tilt of Earth’s axis.

As we enter the wee hours of the morning, Antares, a star we usually associate with later seasons, climbs above the southeastern horizon at 1:42. The first hint of dawn — the start of morning twilight — comes at 3:40 a.m. Mars transits at 4:00, and the elusive planet Mercury rises at 4:08. The Sun finally peeks above the horizon at 5:14 a.m. on the morning of January 16th.

Other Charted InformationMany of the year’s chief astronomical events are listed in the chart’s left-hand margin. Some are marked on the chart itself.


Asunción –10Buenos Aires +54Montevideo +45

Rio de Janeiro –7Santiago +43São Paulo +6

Cape Town +46Durban –3Harare –4

Adelaide +16Brisbane –13Canberra +4

Melbourne +20Perth +18Sydney –4

Johannesburg +8Port Elizabeth +18Pretoria +8

Skygazer’sAlmanac 2012for latitudes near 30° south




For reprints (item SGA12S, $5.95 each postpaid) or

to order a similar chart for north latitude 40° or 50°,

contact Sky & Telescope, 90 Sherman St., Cambridge,

MA 02140, USA; phone +1 617-864-7360, fax +1 617-

864-6117. You can send

e-mail to custserv@

SkyandTelescope.com or



®

SkyandTelescope.com


Opposition of a planet, the date when it is opposite the Sun in the sky and thus visible all night, occurs when its transit line crosses the Equation-of-time line (not the line for midnight). Opposition is marked there by a symbol. For instance, Mars reaches opposition on the night of March 3–4.

Moonrise and moonset can be told apart by whether the round limb — the outside edge — of the Moon symbol faces left (waxing Moon sets) or right (waning Moon rises). Or follow the nearly horizontal row of daily Moon symbols across the chart to find the word Rise or Set. Quarter Moons are indicated by a larger symbol. Full Moon is always a large bright disk whether rising or setting; the circle for new Moon is open. P and A mark dates when the Moon is at perigee and apogee (nearest and farthest from Earth, respectively).

Mercury and Venus never stray far from the twilight bands. Their dates of greatest elongation from the Sun are shown by ◗ symbols on their rising or setting curves. Asterisks mark when Mercury and Venus show their greatest illuminated extent in square arcseconds.

Meteor showers are marked by a star-burst symbol at the date of peak activ-ity and at the time when the shower’s radiant is highest in the night sky. This is often just before morning twilight begins.

Julian dates can be found from the numbers just after the month names on the chart’s left. The Julian day, a seven-digit number, is a running count of days beginning with January 1, 4713 BC. Its first four digits early this year are 2455, as indicated just off the chart’s upper-left margin. To find the last three digits for days in January, add 927 to the date. For instance, on January 15th we have 927 + 15 = 942, so the Julian day is 2,455,942.

Note that the Julian day doesn’t change to this value until 12:00 Univer-sal Time (UT). In Australia, 12:00 UT

falls during the evening of the same day (at 10 p.m. Eastern Standard Time, EST). Before that time, subtract 1 from the Julian day number just obtained.

Time CorrectionsAll events on this southern version of the Skygazer’s Almanac are plotted for an observer at 135° east longitude and 30° south latitude. However, you need not live near McDouall Peak, South Austra-lia, to use the chart. Simple corrections will allow you to get times accurate to a couple of minutes anywhere in the world’s south temperate latitudes.

To convert the charted time of an event into your civil (clock) time, the following corrections must be made. They are given in decreasing order of importance.

• daylight-saving time (“summer time”). When this is in effect, be sure to add one hour to any time obtained from the chart.

• your longitude. The chart gives the Local Mean Time (LMT) of events, which differs from ordinary clock time by many minutes at most locations. Our civil time zones are standardized on par-ticular longitudes. Examples in Australia are 150° E for the eastern states (which use Eastern Standard Time, EST), and 142.5° E for the two central states (an odd value that puts the minute hands of their clocks 30 minutes out of joint with most of the rest of the world).

If your longitude is very close to your standard time-zone meridian, luck is with you and your LMT correction is zero. Otherwise, to get standard time add 4 minutes to times obtained from the chart for each degree of longitude that

you are west of your time-zone meridian. Or subtract 4 minutes for each degree you are east of it. You can look up your longitude on a map.

For instance, Melbourne, Australia (longitude 145°), is 5° west of its time-zone meridian (150°). So at Melbourne, add 20 minutes to any time obtained from the chart. The result is standard time.

Find your Local Mean Time correction and memorize it; you will use it always. The table at far left below has the correc-tions, in minutes, for some major cities.

• rising and setting. Times of rising and setting need correction if your lati-tude differs from 30° south. This effect depends strongly on a star or planet’s declination. (The changing declinations of the Sun and planets can be found in each month’s Sky & Telescope, on the Planetary Almanac page.)

If your site is south of latitude 30° S, then an object with a south declina-tion stays above the horizon longer than the chart shows (it rises earlier and sets later), while one with a north declination spends less time above the horizon. At a site north of 30° S, the effect is just the reverse. Keeping these rules in mind, you can gauge the approximate number of minutes by which to correct a rising or setting time from the table above.

Finally, the Moon’s rapid orbital motion alters lunar rising and setting times slightly if your longitude differs from 135° E. The Moon rises and sets about two minutes earlier than the chart shows for each time zone east of central Australia, and two minutes later for each time zone west of there. Observers in southern Africa can simply shift the Moon symbol a third of the way to the one for the following date. Observers in South America can shift it about halfway there.


Sout

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0° 5° 10° 15° 20° 25°

10° 0 8 16 24 33 43

15° 0 6 12 19 26 33

20° 0 4 8 13 18 23

25° 0 2 4 7 9 12

30° 0 0 0 0 0 0

35° 0 2 5 7 10 13

40° 0 5 10 16 22 29

45° 1 8 17 26 37 49

50° 1 12 25 39 54 72

skygazer’s almanac for latitudes near 40° nort 2012h sga ...€¦ · mar 26 venus reaches...

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